CATransformLayer

CATransformLayer objects are used to create true 3D layer hierarchies, rather than the flattened hierarchy rendering model used by other CALayer classes.

Unlike normal layers, transform layers do not flatten their sublayers into the plane at Z=0. Due to this, they do not support many of the features of the CALayer class compositing model:

Only the sublayers of a transform layer are rendered. The CALayer properties that are rendered by a layer are ignored, including: backgroundColor, contents, border style properties, stroke style properties, etc.